title: Effect of topical naltrexone 0.3% on corneal sensitivity and tear parameters in normal brachycephalic dogs.
abstract: OBJECTIVE
  To determine the effect of topical naltrexone 0.3% on tear production, corneal sensitivity, and tear film stability in normal brachycephalic dogs.
  
  
  METHODS
  Twenty-two normal brachycephalic dogs.
  
  
  METHODS
  Measurements of tear production (Schirmer tear test I and II), intraocular pressure (IOP), central corneal sensitivity (CS), and tear film breakup time (TFBUT) were collected at time 0, 1, and 24 h after administration of either naltrexone (NTX) 0.3% or placebo (SV). Naltrexone or SV was then administered once daily for 1 week, and the above measurements were repeated at 7 days, then again 7 days after discontinuing medication. Owners scored the degree of comfort, redness, rubbing, squinting, and tearing. Serum was collected at time 0, 1, 24 h, and 7 days to determine systemic concentrations.
  
  
  RESULTS
  Owners reported no significant change in the degree of comfort, redness, rubbing, squinting, or tearing. Naltrexone was detected in serum of all treated dogs 1-h postadministration (average: 908 pg/mL, range: 319-1570 pg/mL) and in two dogs at the 1-week time point. Naltrexone was not detected at the 24-h time point. There was no significant effect of NTX on STT1, STT2, IOP, CS, or TFBUT.
  
  
  CONCLUSIONS
  Naltrexone 0.3% is well tolerated and safe when applied topically to the eye once daily. Naltrexone 0.3% did not show any significant effects on corneal parameters as measured in this study. At once, daily dosing NTX is systemically absorbed; however, the degree of systemic absorption is not likely to be clinically significant.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Colorado State University, 300 W. Drake Rd., Fort Collins, CO, 80523, USA.
authors.forename: Trevor S
authors.initials: TS
authors.lastname: Arnold
authors.forename: Luke A
authors.initials: LA
authors.lastname: Wittenburg
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Powell
mesh_terms: D000818:Animals; D003315:Cornea / Q000166:cytology / Q000187:drug effects*; D004285:Dogs; D004334:Drug Administration Schedule; D005260:Female; D007429:Intraocular Pressure / Q000187:drug effects; D008297:Male; D009271:Naltrexone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D009883:Ophthalmic Solutions; D013666:Tears / Q000187:drug effects* / Q000378:metabolism
chemical_list: D009292:Narcotic Antagonists; D009883:Ophthalmic Solutions; D009271:Naltrexone
keywords: brachycephalic; corneal sensitivity; naltrexone; opioid growth factor receptor; opioid-like growth factor; tear production